1. Field of Invention
This invention relates to chains for use in pulling a trolley over a track. More particularly, the invention relates to chains of the type that make horizontal turns and climb and descend grades.
2. Brief Description of the Prior Art
Trolley conveyor systems are known that move trays along a predetermined path defined by a pair of parallel tracks to transport boxed or packaged materials within a storage or production facility. In a prior art conveyor system, a chain consisting of hollow tubular tow bars interconnected by a three axle link incrementally spaced along the predetermined path pulls the trays. The path includes both horizontal turns and climbs and descents in a vertical plane.
The chain in this prior art conveyor system is partially enclosed within a chain rail assembly located intermediate the pair of tracks. The chain rail assembly consists of four separate rails partially enclosing the link. The chain is subject to tension and compression forces as it is separately driven to pull the trays.
The link of the prior art includes a single pair of horizontal wheels, which wheels support the weight of the chain and assist the vertical wheels in guiding the chain along the path. The horizontal wheels are rotatably mounted on one axle and each horizontal wheel travels between upper and lower rails of the chain rail assembly. Two pairs of vertical wheels, which serve to guide the chain along the path and through turns, are mounted on half-link extensions equidistant fore and aft of the horizontal wheels. The extensions are therefore connected to each other by cylindrical bearings on the horizontal wheel axle. The vertical wheels are mounted on the other two axles of the link and also travel between the rails of the chain rail assembly. The axles of the vertical wheels are connected to the tow bars by cylindrical bearings.
The chain therefore follows the path of the chain rail assembly, pulling the trays along the tracks. When the chain must climb a grade, the fore and aft extensions of the link pivot about another cylindrical bearing on the horizontal wheel axle. In making a horizontal turn, the tow bars pivot about the two vertical wheel axles.
It is therefore seen that the prior art conveyor system uses three axles to a link between tow bars. Each axle has a cylindrical bearing. As the chain is pulled along the path of the chain rail assembly, the link is loaded at each of the three axles. Each axle has a cylindrical bearing subject to maximum loading as the chain is pulled along a straight line path and which bearings must be lubricated to reduce associated wear and maintain performance.
The prior art link uses the two pairs of vertical wheels which contact the chain rail assembly to maintain the pair of horizontal wheels at all times perpendicular to a tangent through the curve of a horizontal turn made by the chain rail assembly. However, because the vertical wheels are positioned by and spaced away from the horizontal wheels on extensions, the horizontal wheels do not precisely ride on the chain rails, but ride slightly off of the rails. This in turn subjects the horizontal wheels to some wear as a horizontal turn is made.
It would be advantageous over the prior art to have a link including a single pair of horizontal wheels and a single pair of vertical wheels whose rotational axes intersect at a single point. The prior art link horizontal and vertical wheels act at essentially three points along the length of the link, one for each pair of wheels. Using the three spaced apart pairs of wheels of the link of the prior art, the chain rail assembly often has to follow compelx "S" curves in order for the link of the chain to pull a tray through a simple horizontal turn. If all wheels acted essentially at a single point, the chain rail assembly curve would be a simple horizontal turn and the horizontal wheels would ride on and more precisely follow the path of the chain rail assembly.